Preparation of para-dialkyl substituted aromatic compounds



, United Sta p v,

r 2,916,530 PREPARATION OF PARA-DIALKYL SUBSTITUTED AROMATIC COMPOUNDSHerman S. Bloch, Skokie, Ill., assignor, by mesne assignments, toUniversal ,Oil Products Company, Des

Plaines, 11]., a corporation of Delaware No Drawing. Application October31, 1957 Serial No. 693,506

8 Claims. (Cl. 260-668).,

This application is a continuation in-part of my copending applicationSerial No. 493,060, filed March 8,

1955, now Patent 2,838,581, issued June 10, 1958. This invention relatesto a process for preparing para-dialkyl substituted aromatic compounds,and more particularly to-a process for preparing para-xylene. v

The increased use of terephthalic acid as an intermediate in thepreparation of synthetic fibers of the glycolterephthalic type hasincreased the demand for paraxylene from which the terephthalic acid isprepared. Heretofore, the separation of para-xylene from its orthoandmeta-isomers has been relatively expensive due to difiicultiesencounteredin the process involving the separation of the aforementionedisomers; For example, one method for preparing para-xylene fromethylbenzene and isomers of said para-xylene is to subject the mixture(oxylene, m-xylene, p-xylene and ethylbenzene) to frac- 7 2,916,530 fatentetl Pee. 8, 19 59 One embodiment of the invention is found ina'proces's for the preparation of a p-dialkyl substitutedbenzene whichcomprisescondensin'g propionaldehyde and acetaldehyde in the presenceofa basic condensation'catalyst at a temperature in the range of fromabout 0 to about 150 C., separating the resultant condensation productsfrom the reaction mixture, further'condensing said prodnets with acetonein the presence of a basic condensation catalyst at a temperature in therange of from about 0 to about 125 0., separating and recovering thedesired 7 p-dialkylbenzene.

tional distillation. "However, inasmuch as para-xylene,

meta-xylene and ethylbenzene all boil within a 3 C. range of each other,separation into the variousicomponents by fractional distillation isrelatively diflicult to accomplish.

One-method of operation is to distill out'the orthoxylene which has aboiling point of approximately} to 6 above that-of the other threecomponen ts of the mixture. The paraand meta-xylene alongwith theethylbenzene will then ,be separated into" several fractions,.land paraxylene is then separate'd out by crystallization from cuts Anothermethod of containing the highest percentage.

separating the para-xylene from the unwanted isomers is Y to displacethe eutectic compositions of paraand metaxylenes by the addition of aco-crystallizing agent such as carbon tetrachloride followed by cooling,the para-xylene and carbon tetrachloride thereby separating out of themixture, and thereafter recovering said para-xylene by fractionaldistillation of the para-xylene-carbon tetrah r em t J t Still. anothermethod of recoveringparaxylene'is to partially sulfonate the mixture,separate the unsulfonated layer from the reaction mixture and-,crystallize the para-v xylene from the mixture by lowering thetemperature.

It can readily be seen from the above description that obtainingrelatively pure para-xylene for the manufacture of terephthalic acidinvolves many steps which, as hereinbefore set forth, are relativelydiflicult and expensive to accomplish. Y

It is therefore an object of this invention to providea relativelyinexpensive and novel process for obtaining para-dialkyl substitutedaromatic compounds. 1

Agfurther object of this invention. is atoproviclev a process,-

for preparing para-dialkyl substituted: aromatic compounds such aspara-xylene by condensing specific ketones and aldehydes.

A specific object of this invention is to provide a process forpreparing para-xylene by condensing, in separate stages,acetone,'acetaldehyde and propionaldehyde and separating the desiredpara-xylene from any ortho- Xylene which may form therein. 1

. X -OH CHO in which X comprises either ahydrogen A specific embodimentof the invention resides in .a

process for the preparation of p-xylene .which comprises condensingequimolar proportions of propionaldehyde and 2 acetaldehyde in thepresence of a basic condensationcata.

lyst at a temperature in the range of from about 0 to about 150 C.,separating the resultant 2.-methyl-3-hy-.

droxybutyraldehyde and 3-hydroxyvaleraldehyde from the reaction mixture,further condensing the same with an equimolar proportion of acetone inthe presence of a basic condensation catalyst at a temperature in therange: of from about 0 toabout 125 (3., separating andre covering'thedesired p-xylene.

A more specific embodiment of the invention is found in a process forthe preparation of p-xylene which com-. prises condensing equimolarproportions of propional dehyde and acetaldehyde in the presence ofpotassium carbonate at a temperature in the range of from about 0 toabout 150 'C., separating the resultant 2-methyl35hy-jd'roxybutyraldehyde and 3-hydroxyvaleraldehyde from the reactionmixture, further condensing the same with an equimolarproportion ofacetone in the presence of a basic condensation catalyst at atemperature in the range of from about 0 to about 125 C., separatingp-xylene' from o-xylene, and recovering the former. I

Other objects and embodiments referring to alternative basiccondensation catalysts will be found in the following.

further detailed description of the invention. I

' It is now proposed that polyalkyl substituted, and par ticularly,orthoand para-dialkyl substituted aromaticcompounds be prepared. byreacting or condensing equimolar quantities of ketones and aldehydes,the particular reactants .u sed being dependent upon the length andnumber of the alkyl' sub'stituents desired on the aromatic ring.

Onepf the aldehydic r'eactantswhich may be used in this invention is analdehyde having the general formula radical, a halogen, nitro, sulfo,carboxy, carboxamido, by droxy, etc. radical, or a hydrocarbon radicalor hydrocarbon radicahcontaining a" substituent hereinbefore enu-'merate'd; The other aldehydic reactant used in'the ref 7 action has thegeneral formula:

' in whichX Y Z are independently selected from those substituentsalready'listed above. The remaining reactant comprises a ketone havingthe general formula:

acetaldehyde fi-chloropropionaldehyde, fifi-dichloropropionaldehyde,fi-nitropropionaldehyde, fi-sulfopropionaldehyde,9,,8,5-trichloropropionaldehyde, a,adichloroacetone, etc., although notnecessarily with equivalent results. It is to be understood that theabove mentioned com pounds are only examples of the aldehydes andketones which may be used in this process and that said process is notnecessarily limited to said compounds.

The reactions of this invention may be effected in the formate, cesiumformate, magnesium formate, calcium formate, barium formate, strontiumformate, lithium carbonate, potassium carbonate, sodium carbonate,rubidium carbonate, cesium carbonate, magnesium carbonate, calciumcarbonate, barium carbonate, strontium carbonate, lithium hydroxide,potassium hydroxide, sodium hydroxide, rubidium hydroxide, cesiumhydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide,strontium hydroxide, etc.

The initial condensation reaction between the aldehydes is carried outat temperatures in the range of from about. to about 150 C. andpreferably at a temperature in the range of from about 40 to about 70 C.In addition the reaction takes place at atmospheric pressure; however,if higher temperatures are to be used the pressures are in-' creased,said pressure used being in the range of from about 2 to about 100atmospheres or more, the pressure being sufiicient to maintain at leasta portion of the reactants in the liquid phase. The second condensationstep of the reaction between the condensation product of the firstreaction and the desired ketone will take place under conditions similarto those hereinbefore set forth for the first reaction step.

The products resulting from the condensation of equimolar proportions ofacetone, acetaldehyde and propionaldehyde as described herein comprise amixture of oand p-xylene, which due to the relatively wide disparity inboiling points (o-xylene boiling at 144.4 C. and p-xylene boiling at138.4 C.) enables the two xylenes to be easily separated by fractionaldistillation.

The reaction of this invention may be efiected in any suitable mannerand may comprise either a batch or continuous type operation. When abatch operation is used, a quantity of each of the starting materials inequimolar proportions is placed in asuitable reaction vessel containingthe desired catalyst. The vessel is then heated to the desiredtemperature and maintained thereat for a predetermined residence time.At the end of this time, the vessel and contents are cooled to roomtemperature and the reaction product separated by conventional means,such as fractional distillation.

When a continuous type operation is used, the starting materials areeach continuously charged, in a separate stream, or two combined in onestream while the other is independently and subsequently admitted, to areactor containing the desired catalyst and maintained at suitableoperating conditions of temperature and pressure. The reactor may be anunlined vessel or coil or may contain an adsorbent material such as firebrick, dehydrated bauxite, or the like. Upon completion of the desiredresidence time, the products of the reaction comprising the oandp-dialkyl substituted aromatic compounds are continuously withdrawn andsubjected tov fractional distillation whereby the p-dialkyl substitutedaromatic compound is. separated from the o-dialkyl substituted aromaticcompound and/ or unreacted starting materials or intermediates which maybe present. 'In the. preferred type of operation, as hereinafterdescribed, two of the reactants are allowed to form condensationproducts, these are removed and by fractional distillation a fractioncomprising the condensation product of one mol of each of the reactantsis recovered from those by-products formed from two mols of one of thereactants, and said fraction is then allowed to react with the thirdreactant to form the desired end-products (i.e., orthoandparadisubstituted aromatic hydrocarbons) which are then easily separatedby fractionation.

This preferred continuous type of operation is used in order to minimizethe interaction of two mols of any of the reactants with 1 mol of theother reactant, said reaction resulting in a yield of undesired sideproducts or less valuable reaction products. For example, theinteraction of 2 mols of acetone or 2 mols of propionaldehyde with 1 molof acetaldehyde would result in the production of m-xylene, aparticularly undesirable product in the preparation of p-xylene, due tothe fact that the m-xylene and p-xylene boil within 1 C. of each other.

Yet another alternative which may be used is to add the. third componentof the reaction mixture down-stream of the point of introduction of thefirst two reactants in the same reactor, although this alternativegenerally gives lower yields of the desired products than the previousmethod in which the bimolecular intermediate condensation product isseparately recovered and then subjected to further reaction.

In the interaction of acetaldehyde, propionaldehyde, and acetone to makexylenes, the reaction may be regarded as occurring in twostagesinteraction of two of the components as a first stage, andcondensation of the intermediate product with the third component as asecond stage. If all three reactants were to be mixed and the reactionwere to proceed non-selectively, the purpose of this invention would bedefeated, since equal amounts of ortho-, metaand para-xylenes would beformed and there would be, in addition, considerable amounts ofopen-chain by-products and condensation products containing fewer ormore than eight carbon atoms. The pre ferred method of operation avoidsthese undesirable possibilities by a careful control of the order inwhichthe reactions are allowed to proceed. This order is determined fromthe following considerations:

If the intial intermediate reaction is to be one between propionaldehydeand acetone, the two intermediates will be E (A). and

(CH:)2(I3-CH-CHO (A) on condensation with acetaldehyde, ring closure,and dehydration yields para-Xylene; (B) yields orthoxylene. molecularcondensation products of two mols of acetone (diacetone alcohol) and oftwo mols of propionaldehyde,

CHaCH-CHafi-CHI and (CH:):?--CHr- CHO O H ('D).

But (A) and (B) are contaminated with bi-.

Both of these fiveicarbon-intermediates should beea'sily separable fromaldol and diacetone alcohol formed as a result of theconcurrent'condensation'of two mols of acetaldehyde or two mols ofacetone; respectively. But ofthe two intercondensation products (C) and(D), it is found that (C) is formed preferentially; and (C), oninteraction with propionaldehyde yields ortho-xylene or open-chainproducts, while (D) yields para-xylene; The yields of para-xylene bythis route aretherefore poorer than desirable (althoughgood'yields ofortho-xylene may be obtained) and it is not the preferred "method forpreparing para xylene. :v 3 3 The third (and preferred) initialreactionis that between acetaldehyde and propionaldehyde. Here again,two intercondensationproducts are possible, and these, since, theycontain five carbon atoms, are separable without difliculty from thefour carbon or six carbon products formed by condensation-of two mols.of either of the reactants. The intercondensation products. are:v

CHs-OH-CH-CHO '11 H. p (E) cm-omon on -ono Eighty-eight g. ofacetaldehyde and 116 g. ofpropionaldehyde are placed in a glass liner ofa rotating autoclave having an 850 cc. capacity along with 5 g. ofpowdered anhydrous potassium carbonate. The glass liner is placed in theautoclave which is thereafter sealed and the reaction is allowed toproceed for 24 hours while said autoclave and contents thereof aremaintained at about 50 C. At the end of this time the autoclave andcontents thereof are cooled and the reaction products removed, washedand distilled. A fraction comprising the material boiling at 87-97 C.(20 mm.) is recovered (weight, 105 g.). This material is mixed with 60g. of acetone, and to the mixture is added 5 g. of anhydrous potassiumcarbonate. The mixture is maintained at a temperature of about 60 C. andstirred for 20 hours. At the end of this time the reactor and contentsthereof are allowed to return to room temperature and the reactionproduct is distilled, yielding a fraction boiling at 135-145 C. whichweighs 48 g. and contains approximately 70% p-xylene and 30% o-xylene,which is redistilled to yield a fraction of pure p-xylene boiling at138-139" C.

Example [I Example] v Eighty-eight g. of acetaldehyde and 116 g. ofpropionaldehyde are placed in a glass liner of a rotating autoclavealong with 5 g. of sodium carbonate. The autoclave is sealed and heatedto a temperature of approximately 50 C. and maintained thereat for aperiod of about 24 hours, at the end of which time the autoclave andcontents thereof are allowed to cool to room temperature. The reactionproducts are removed, washed and subjected to fractional distillationunder reduced pressure. The fraction boiling at 87-97 C. (20 mm.) isrecovered. This fraction is mixed with 60 g. of acetone and 6 g. ofsodium carbonate after which the mixture is maintained at a temperatureof about 55 C. for an additional 20 hours. The reaction product fromthis condensation is subjected to fractional distillation yielding afraction boiling at -145 C. Which, like the reaction product of Ex ample1, contains approximately 70% p-xylene and 30% o-xylene. 'This fractionis again subjectedtofractional distillation and the cut boiling at138-139" C., comprising pure p-xylene, is separated and recovered.

Example III Example IV Eighty-eight g. of acetaldehyde and 116 g. ofpropion aldehyde are condensed in the presence of 5 g. of calcium oxidein a manner similar to that set forth above. The

desired reaction product, comprising a mixture of 2-.

methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde, is recoveredand further condensed with acetone in the presence of anadditionalamount of calcium oxide. The desired reaction product comprising p-xylene, is recovered by conventional means.

Example V A mixture of acetaldehyde and propionaldehyde in the presenceof potassium formate is subjected to reaction conditions similar to thatset forth in Example I above. The reaction product of this condensation,comprising a mixture of 2-methyl-3 hydroxybutyraldehyde and 3hydroxyvaleraldehyde, is removed, washed and distilled. The fractionboiling between 87-97 CL (20 mm.) is recovered and further condensedwith 60 g. of acetone in the presence of 5 g. of potassium formate,Thecondensation product of this reaction is treated in a manner similarto that set forth above, the desired product, comprising p-xyleneboiling at a temperature in the range of from about l38-139 C. beingseparated and recovered by fractional distillation.

I claim as my invention:

1. A process for the preparation of p-xylene which comprises condensingpropionaldehyde and acetaldehyde in the presence of a solid basiccondensation catalyst selected from the group consisting of the alkalimetal and alkaline earth metal formates, acetates, carbonates,hydroxides and oxides at a temperature in the range of from about 0 toabout C., separating the resultant condensation products from thereaction mixture, further condensing said products with acetone in thepresence of a solid basic condensation catalyst selected from the groupaforesaid at a temperature in the range of from about 0 to about 125 C.,separating and recovering the desired p-xylene.

2. A process for the preparation of p-xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of a solid basic condensation catalyst selected from the groupconsisting of the alkali metal and alkaline earth metal formates,acetates, carbonates, hydroxides and oxides at a temperature in therange of from about 0 to about 150 C., separating the resultantcondensation products from the reaction mixture, further condensing saidproducts with an equimolar proportion of acetone in the presence of asolid basic condensation catalyst selected from the group aforesaid at atemperature in the range of from about 0 to about 125 C., separating andrecovering the desired p-xylene.

3. A process for the preparation of p-xylene which comprises condensingequimolar proportions of pro pionaldehyde and acetaldehyde in thepresence of a solid basic condensation catalyst selected from the groupconsisting of the alkali metal and alkaline earth metal formates,acetates, carbonates, hydroxides and oxides at a temperature in therange of from about to about 150 C., separating the resultant2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from thereaction mixture, further condensing the same with an equimolarproportion of acetone in the presence of a solid basic condensationcatalyst selected from the group aforesaid at a temperature in the rangeof from about 0 to about 125 C., separating and recovering the desiredp-xylene.

4. A process for the preparation of p-Xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of solid sodium carbonate at a temperature in the range of fromabout 0 to about 150 C., separating the resultant 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from thereaction mixture, further condensing the same with an equimolarproportion of acetone in the presence of solid sodium carbonate at atemperature in the range of from about 0 to about 125 C., separating andrecovering the desired p-xylene.

5. A process for the preparation of p-xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of solid potassium carbonate at a temperature in the range offrom about 0-to about 150 C., separating the resultant2-methyl-3-hydroxybutyraldehyde and 3-hydroxyva1era1- dehyde from thereaction mixture, further condensing the same with an equimolarproportion of acetone in the presence of solid potassium carbonate at atemperature in the range of from about 0 to about 125 C., separating andrecovering the desired p-xylene.

6. A process for the preparation of p-xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of solid potassium acetate at a temperature in the range offrom about 0 to about 150 C., separating the resultant 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from thereaction 'rnixture, further condensing the same with an equimolarproportion of acetone in the presence of solid potassium acetate at atemperature in the range of from about 0 to about C., separating andrecovering the desired p-xylene.

7. A process for the preparation of p-xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of calcium oxide at a temperature in the range of from about 0to about C., separating the resultant 2-methyl-3- hydroxybutyraldehydeand S-hydroxyvaleraldehyde from the reaction mixture, further condensingthe same with an equimolar proportion of acetone in the presence ofcalcium oxide at a temperature in the range of from about 0 to about 125C., separating and recovering the desired p-xylene.

8. A process for the preparationof p-xylene which comprises condensingequimolar proportions of propionaldehyde and acetaldehyde in thepresence of solid potassium formate at a temperature in the range offrom about 0 to about 150 C., separating the resultant 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from thereaction mixture, further condensing the same with an equimolarproportion of acetone in the presence of solid potassium formate at atemperature in the range of from about 0 to about 125 C., separating andrecovering the desired p-xylene.

OTHER REFERENCES Noller: Chemistry of Organic Compounds, 1951, N. B.Saunders Co., Phila., Pa., pages 203 and 206 only relied on. 1

1. A PROCESS FOR THE PREPARATION OF P-XYLENE WHICH COMPRISES CONDENSINGPROPIONALDEHYDE AND ACETALDEHYDE IN THE PRESENCE OF A SOLID BASICCONDENSATION CATALYST SELECTED FROM THE GROUP CONSISTING OF THE ALKALIMETAL AND ALKALINE EARTH METAL FORMATES, ACETATES, CARBONATES,HYDROXIDES AND OXIDES AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0* TOABOUT 150* C., SEPARATING THE RESULTANT CONDENSATION PRODUCTS FROM THEREACTION MIXTURE, FURTHER CONDENSING SAID PRODUCTS WITH ACETONE IN THEPRESENCE OF A SOLID BASIC CONDENSATION CATALYST SELECTED FROM THE GROUPAFORESAID AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0* TO ABOUT 125*C., SEPARATING AND RECOVERING THE DESIRED P-XYLENE.